The objective of this experimentation is to determine the developmental potential of embryonic stem (ES) cells in the rhesus monkey. Such a measure of developmental potential is considered essential to the long term objective of using ES cells clinically, to repair or replace damaged or diseased tissues or organs. Specific aims include 1) documentation of the participation of rhesus monkey ES cells in the preimplantation development of chimeric embryos in vitro. Chimeric embryos will be produced by injecting ES cells, transfected with a beta-galactosidase reporter gene construct, into diploid 4-8 cell stage embryos or by injecting non-transfected, ES cells into 4-8 cell stage, tetraploid embryos. The participation of ES cell progeny in the ICM and trophectoderm of the resulted chimeric blastocysts in vitro will be confirmed in individual cells by beta-galactosidase activity or by the determination of ploidy using fluorescent In situ hybridization (FISH). Following achievement of this aim, efforts will focus on 2) a determination of the contribution of ES cell progeny to specific cell lineages in chimeric rhesus monkeys. Chimeric embryos produced by injection of nontransfected ES cells into normal diploid embryos, as well as chimeras produced under specific aim 1, will be transferred into synchronized surrogates by a non-surgical, transcervical procedure. The tissue distribution of ES cell derivatives in the resultant fetal, neonatal or infant monkeys will be determined by genetic analysis, beta-galactosidase activity or by FISH determination of ploidy. This research will enhance stem cells as a model biological system adding specific new information on the developmental potential of ES cells from 8 separate rhesus monkey ES cell lines currently available in this laboratory.